- #1
djester555
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Going Up An elevator cab in a New York hotel has a total run of 185 m. Its maximum speed is 261 m/min. Its acceleration (both speeding up and slowing down) has a magnitude of 1.21 m/s2.
(1) How far does the cab move while accelerating to full speed from rest?
v = 261m/min
= 261m/min * (1/60)min/s
= 261/60 m/s
= 4.35m/s
a = 1.21m/s^2
a) u = 0
v^2 = u^2 + 2ad
so
v^2 = 2ad
d = v^2 /2a ≈ 7.8192m
(2) How long does it take to make the nonstop 185 m run, starting and ending at rest?
so d = 2*7.8192 = 15.6384m all together
d = (1/2)a(t1)^2
so
t1 = √(2d/a) ≈ 5.08414s
spends D = 185 - 15.6384 = 169.3616m at constant velocity v=4.35m/s
D = vt2
so
t2 = D/v ≈ 38.9337s
therefore
T = 5.08414 + 38.9337 = 44.01784s all up
The issue i'am having is with question 2. From some reason 44.01784 isn't right, what am i doing wrong. i know my first answer is correct
(1) How far does the cab move while accelerating to full speed from rest?
v = 261m/min
= 261m/min * (1/60)min/s
= 261/60 m/s
= 4.35m/s
a = 1.21m/s^2
a) u = 0
v^2 = u^2 + 2ad
so
v^2 = 2ad
d = v^2 /2a ≈ 7.8192m
(2) How long does it take to make the nonstop 185 m run, starting and ending at rest?
so d = 2*7.8192 = 15.6384m all together
d = (1/2)a(t1)^2
so
t1 = √(2d/a) ≈ 5.08414s
spends D = 185 - 15.6384 = 169.3616m at constant velocity v=4.35m/s
D = vt2
so
t2 = D/v ≈ 38.9337s
therefore
T = 5.08414 + 38.9337 = 44.01784s all up
The issue i'am having is with question 2. From some reason 44.01784 isn't right, what am i doing wrong. i know my first answer is correct